GB2247234A - Fluid loss reduced cement compositions - Google Patents

Abstract

Cementing compositions having improved fluid loss capabilities, comprise a hydraulic cement, water, a styrene/ butadiene latex and a surfactant, wherein the latex is present in the composition in an amount of from about 4 to about 35 percent latex by weight of said hydraulic cement, and the weight ratio of styrene to butadiene in said latex is from about 20 to 80 to about 30 to 70; the surfactant is a compound having the general formula H(CH2)d (OC2H4)6 SO3X wherein X is any compatible cation, d is from about 5 to about 20 and e is from about 10 to about 30, said surfactant being present in said composition in an amount of from about 5 to about 40 percent surfactant by weight of said latex; and said water is present in said composition in an amount of from about 20 to about 150 percent water by weight of said hydraulic cement. The compositions are used for cementing conduits in well bores. <IMAGE>

Description

FLUID LOSS REDUCED CEMENT COMPOSITIONS The present invention relates to a cement slurry composition and to its use for cementing wellbores penetrating a subterranean formation.

In the production of hydrocarbons from a subterranean formation, the subterranean formations are typically cemented or sealed by pumping an aqueous hydraulic cement slurry into the annulus between the pipe and the formation. In the oft practiced placement of cement in the annular space between the casing of an oilwell and the surrounding subterranean formation, the cement slurry is commonly pumped into the casing and back up the annular space outside the casing. Occasionally, the cement is introduced directly to the annular space at the outer side of the casing. Where the cement has been pumped down the casing initially, any cement slurry which remains in the casing is displaced into the annulus by a suitable fluid or fluids.

On some occasions, the zones adjacent the cement containing annulus contain connate gas under substantial pressure. In these instances, an undesirable phenomenon referred to in the art as gas leakage is sometimes encountered in which the formation gas enters the annular space which surrounds the well casing after the primary cementing slurry has been placed. This gas can migrate to the surface, or other subterranean zones, through the annulus and the cement, forming a permanent flow channel or a highly permeable cement and the leakage is detrimental to the long term integrity and sealing efficiency of the cement in the annulus and the magnitude of such leakage is often enough to require an expensive remedial squeeze cementing job to be carried out to suppress or stop the gas leakage.Such gas leakage can cause high volume blow-outs shortly after the cement placement and before the cement has initially set.

Gas leakage occurs even though the initial hydrostatic pressure throughout the column of the cement slurry placed in the annulus far exceeds the pressure of gas in the formation from which the leaking gas originates. In explanation, it is theorized that two different wellbore conditions can occur which will allow gas entry into the annulus. The first condition which is believed to be a prerequisite for annular fluid-gas migration is gellation of the cement slurry and subsequent development of static gel strength.

This condition starts shortly after the cement slurry becomes static. The pressure required to move the cement is then directly related to the column length and the static gel strength. Thus as static gel strength increases, there is a loss of ability to transmit hydrostatic pressure.

The second condition which contributes directly to the loss of pressure in the cement column (and across the pressurized gas zone) is the loss of fluid and volume reduction within the cement column. This condition is believed to be due to the leak-off of water in the cement into the formations and from cement volume reduction due to the cement hydration.

Volume reductions occurring after static gel strength starts to develop results in a loss of pressure in the cement column. As the pressure in the cement column drops below the gas pressure, gas will enter the annulus. If at this time the static gel strength is still below the gas percolation value, a gas leakage condition is created.

Interestingly, the gelled or partially set cement, although it is incapable of maintaining or transmitting full hydrostatic pressure, still is not sufficiently rigid or set to prevent the entry of gas into the annulus and the upward percolation of the gas. According to the most popular theories, an absolute volume reduction occurring after the cement column can no longer transmit full pressure reduces the pore pressure of the still semi-plastic slurry. When the pore pressure falls below the formation gas pressure, formation gas leaks into the wellbore and if the cement is not gelled enough to prevent percolation, gel leakage channels are formed. Two principal mechanisms which act to decrease the pore pressure are the hydration reaction of cement and the loss of filtrate to the adjacent permeable formation.

Gas leakage problems have been noticed following casing cementing operations on surface conductors and intermediate, production and liner jobs. Gas returns to the surface have often been noticed within one to seven hours after placement of the cement. Many times, however, the gas flow does not return to the surface, but flows into low pressure zones causing interzonal gas communication.

Another problem experienced when conventional cement slurries are utilized in cementing wellbores in a subterranean formation concerns the susceptability of the cement to attack by corrosive fluids. The corrosive fluids may be introduced into the subterranean formation by a treatment performed from the surface, such as injection of acidizing fluids to enhance formation permeability or carbon dioxide to energize or thin hydrocarbon fluids in the formation or generated downhole by reaction of various compounds such as in various insitu mining processes or the corrosive fluid may be naturally present in the formation such as hydrogen sulfide in some oil-bearing formations.

Yet another problem concerns the behavior of conventional cement slurries when exposed to elevated temperatures in the subterranean formation. As the temperature increases, the cement slurry begins to thin and settling of the heavier particles in the slurry can occur. This results in poor or incompetent cement bonds within the subterranean formation. Conventional practice would dictate the use of a material to viscosify the cement slurry to slow the settling process. Unfortunately, addition of viscosifying materials can make mixing of the cement slurry at ambient conditions of the surface extremely difficult or even impossible.

One partial solution has been the composition disclosed in U.S. Patent 4,537,918 which comprises water, hydraulic cement, a styrene-butadiene copolymer latex (70-30 to 30-70 weight percent ratio) and a latex stabilizer selected from the group of (i) lignosulfonates and their partly desulfonated derivatives, (ii) sulfonic acid or sulfite modified malamine-formaldehyde resins, (iii) formaldehyde/sulfonate naphthalene resins and (iv) condensation products of binuclear sulfonated phenols and of formaldehyde. This system is limited in that only the particular styrene/butadiene latices will function in the composition. Too large a quantity of butadiene provokes premature coagulation of the latex and too much styrene prevents film formation in the slurry. This patent also generally describes the prior uses in which latex latices have been employed in the oil and gas industry. Although latices have been utilized in the oil industry, the compositions which have been recommended have been unable to solve the gas migration problem because of difficulties of pumping, flocculation of the latex, uses limited to low temperatures and particular latice ratios.

We have now devised a cement composition which is effective from low temperatures of from about 300F (-10C) to temperatures in excess of 4500F (2320C) and by which many of the problems or limitations of the prior art compositions are mitigated.

According to the present invention, there is provided a cement slurry composition having improved fluid loss control properties, which comprises a hydraulic cement, water, a styrene/butadiene latex and a surfactant, wherein the latex is present in the composition in an amount of from about 4 to about 35 percent latex by weight of said hydraulic cement, and the weight ratio of styrene to butadiene in said latex is from about 20 to 80 to about 30 to 70; the surfactant is a compound having the general formula H(CH2)d (OC2H4)e SO3 X wherein X is any compatible cation, d is from about 5 to about 20 and e is from about 10 to about 30, said surfactant being present in said composition in an amount of from about 5 to about 40 percent surfactant by weight of said latex; and said water is present in said composition in an amount of from about 20 to about 150 percent water by weight of said hydraulic cement. The invention also includes a method of cementing a conduit in a wellbore penetrating a subterranean formation comprising introducing a cement slurry composition into the annulus between said conduit and said formation and permitting said cement slurry to set, the temperature of said formation being from about 300F (-10C) to about 4500F (2320C) and contains gas under pressure wherein the cement slurry composition is a composition of the invention.

When the compositions are to be used at temperatures above 2000F (930C), a stabilizer and retarder comprising a selected copolymer of AMPS /acrylic acid also preferably is present (AMPS is a trademark of The Lubrizol Corporation for 2-acrylamido-2-methylpropanesulfonic acid).

The term "cement" or "hydraulic cement" as used herein is intended to include those compounds of calcium, aluminium, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such compounds include, for example, Portland cement and particularly Portland cement of API classes G and H, although other classes may be utilized, pozzolan cements, gypsum cements, high alumina content cements, silicate cements and high alkalinity cements can be utilized in various applications of the present invention.

Portland cements are preferred.

The water utilized in the cement composition can be water from any source provided that it does not contain an excess of any compounds that effect the stability of the cement composition of the present invention. The water can contain various salts such as sodium, potassium or calcium chloride and the like. Depending upon the particular cement slurry being formed and the intended conditions of use, the water is utilized in the cementing composition in an in the range of from about 20 to about 150% by weight of dry cement.

The latex is selected from styrene/butadiene latices and more particularly from styrene(10-908 by weight) / butadiene (90-10% by weight) and particularly those having the ratio of about 20/80 to about 80/20 and most particularly those having a styrene/butadiene ratio of from about 20/80 to about 30/70. It is understood that the styrene/butadiene latice described above generally is commercially produced as a terpolymer latex and the definition of the latex as used herein also is intended to include such terpolymer latices which include from about 0 to 3% by weight of a third monomer to assist in stabilizing the latex emulsion. The third monomer, when present, generally is anionic in character and has a carboxylate, sulfate or sulfonate group.

Other groups that may be present on the third monomer include phosphates, phosphonates or phenolics. Nonionic groups which exhibit steric effects and which contain long ethoxylate or hydrocarbon tails also can be present.

The most preferred ratio has been found to provide excellent fluid loss control to a cement slurry without premature coagulation or loss of compressive strength in the set cement. Latex latices of the type described above are available, for example, from Unocal Chemicals Division of Unocal Corporation, Chicago, Illinois or Reichhold Chemicals, Inc. Dover, Delaware.

The latex is present in the composition in an amount of from about 4 to about 35% by weight of dry cement.

Preferably, the latex is present in the composition in an amount of from about 15 to about 25% by weight of dry cement.

The surfactant present in the composition comprises a compound of the general formula H(CH2)d(OC2H4)eS03- X+ wherein d is from about 5-20, e is from about 10 to about 40 and X is a compatible cation. A preferred surfactant is the sodium salt having the chemical formula H(CH2)12-15(OC2H4)15S03-Na+ which is commercially available from PPG-Mazer, Gurnee, Illinois. The surfactant is present in the composition in an amount of from about 5 to about 40% by weight of latex present and preferably is present in an amount of from about 10 to about 25% by weight of latex.

Other types of well known and conventional additives also can be incorporated into the cement slurry composition to modify the properties of the composition.

Such additives include additional fluid loss control additives such as, for example, cellulose derivatives such as carboxymethylhydroxyethyl cellulose, hydroxyethyl cellulose, modified polysaccharides, polyacrylamides, guar gum derivatives, AMPS copolymers, polyethyleneamine and the like.

Dispersing agents can be utilized to facilitate using lower quantities of water and to promote higher set cement strength. Friction reducers which promote freer movement of the unset composition can be incorporated in amounts up to about several percent by weight of dry cement.

Defoaming or antifoaming agents can be utilized in the composition to reduce or substantially eliminate foaming upon formation of the cement slurry. The defoamer can comprise substantially any of the compounds known for such capabilities such as the silicon oil compounds. Such agents generally would be admixed with the cement slurry in an amount of from about 0.02 to about 0.08 gal. per sack (.00lie to about .0072m3/kg) of dry cement.

Accelerators, such as the soluble inorganic salts in addition to calcium chloride, can be utilized in an amount of up to several percent by weight of the dry cement in various situations.

Retarders may be utilized when the bottom hole circt31ating temperature exceeds 100F (66 0C). Retarders satisfactory for use in the present invention include those commercially available products commonly utilized as retarders. Examples include lignosulfonates such as calcium lignosulfonate and sodium lignosulfonate; organic acids such as tartaric acid and gluconic acid and the like. The proper amount of retarder required in any particular case should be determined by running a "thickening time" test for the particular retarder and cement composition being utilized. Such tests may be run in accordance with the procedures set forth in API Specification For Materials And Testing For Well Cements, API Spec. 10.Generally, "thickening time" is defined in Spec. 10 as the elapsed time from the time pumping begins until the cement reaches from about 70 to 100 units of consistency. In most applications, the amount of retarder, if any, required will not exceed 6 percent by weight of the dry cement.

A particularly preferred retarder is a copolymer or copolymer salt of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid. The copolymer comprises from about 40 to about 60 mole percent AMPS with the balance comprising acrylic acid. The copolymer has an average molecular weight below about 5000. This retarder preferably is utilized in the composition when the bottom hole circulating temperature exceeds about 200 F.(93 C). Suprisingly, this retarder has been found to both retard the setting of the cement at the elevated formation temperatures and to stabilize the latex latice against agglomeration or inversion at the elevated temperature. The copolymer can be present in the cement composition in an amount of from about 0.05 to about 3% by weight of dry cement.

Weighting agents such as various oxides of iron, barite, titanium and the like may be present in amounts of from about 0 to about 70t by weight of dry cement.

Lightening agents such as pozzolana, fly ash, silica glass or ceramic microspheres and the like also may be utilized in amounts up to about 50% by weight of dry cement.

Silica may be present in amounts of from about 0 to 50% by weight of cement and preferably from about 0 to 35% by weight of cement when a slurry with improved strength at elevated temperatures is desired. Preferably, the silica has a particle size in the range of less than about 40 mesh (0.420mm sieve aperture! on the US Sieve Series.

The composition of the present invention may be utilized in formations having bottom hole circulating temperatures of from about 300F. (-10C) to in excess of about 4500F. (2320cm.

The composition of the present invention may be prepared in accordance with any of the well known mixing techniques so long as the latex and surfactant are not directly admixed without prior dilution by other liquids present. In one preferred method, the water is introduced into the cement blender and the defoamer, if present, surfactant and latex then are sequentially added with suitable agitation to disperse the constituents. Any other liquid additives then may be admixed with the slurry.

Thereafter, the cement and any other dry solids are added to the blender and agitated for a sufficient period to admix the constituents. The amount of each constituent of the cement composition utilized in forming the cement slurry will depend upon the temperature level to be experienced, rheological considerations and the other additives that are present.

The cementing compositions of the present invention are useful in subterranean formation cementing operations and particularly oil, gas and water well cementing operations since the compositions have reduced fluid loss to the surrounding formation. The reduced fluid loss substantially maintains the hydraulic head of the cement column in the wellbore whereby gas migration into the wellbore from the surrounding formation is minimized or substantially prevented. The cement is utilized by introducing the cement composition into the space between the conduit or casing placed in the wellbore and the face of the wellbore penetrating the subterranean formation.

Tn order that the invention may be more fully understood.

the following Example is given by way of illustration only.

EXAMPLE I The following tests were performed to determine the utility of the composition of the present invention.

Test slurries were prepared by admixing the liquid additives one at a time with water in a blender. Each liquid additive was mixed for 20 seconds at 4000 RPM before the next additive was introduced. Thereafter, the dry additives were admixed with the liquid in the blender within 5 seconds while mixing at 4000 RPM and then the blender was operated at 12000 RPM for 35 seconds as per the procedures specified in API Spec 10, Fourth Ed August 1, 1988, in the API Specification For Materials And Testing For Well Cements, to form a cement slurry test sample.

Thickening time testing, when performed, was in accordance with the procedures set forth in API Spec 10.

Rheological properties, when determined, were determined in accordance with the procedures outlined in API Spec 10.

In general, the cement sample was placed in an atmospheric consistometer which was preheated to the test temperature and stirred for 20 minutes. The atmospheric consistometer in a nonpressurized device that simulates a cement pumping process via movement of a consistometer can about a paddle.

The temperature of the test may be varied. The consistency of the cement is measured in terms of Bearden units of consistency (Bc). A pumpable cement slurry should measure in the range of from about 2-30 Bc and preferably from about 2 to 12-15 Bc. Cement slurries thicker than these ranges become progressively more difficult to mix and pump.

Slurries thinner than 3-5 Bc will tend to exhibit undesirable particle settling and free water qeneration.

Fluid loss is measured at 1000 psi (6.89spa! through a 325 mesh (aperture 0.044mm) screen on the US Sieve Series in cc/30 minutes as more fully described in API Spec 10.

Solids suspension capability, when determined, requires the prior performance of the above-identified thickening time testing for the cement slurry sample. In general, after the thickening time for the cement slurry has been determined, a second test is initiated in the same equipment using the appropriate temperature and heating rate schedule.

When the schedule specified time to reach final test temperature and pressure has been reached plus 15 minutes, the slurry viscosity in consistency units is noted and the slurry cup drive motor is turned off for 10 minutes. The final temperature and pressure are maintained throughtout the remainder of the test. At the end of the 10 minute static period the slurry cup drive motor is turned on and the maximum viscosity when movement begins is noted in consistency units. After the test time has reached 50% of the cement slurry's thickening time as previously determined, the slurry cup drive motor is shut off again for 10 minutes and the viscosity is noted. At the end of 10 minutes, the slurry cup drive motor is started and the maximum viscosity when movement begins is noted. The slurry then is stirred until the test time has reached 75% of the cement slurry's thickening time. After which the drive motor is again stopped and the viscosity is noted. After 10 minutes the motor is restarted and the maximum viscosity is noted and the motor is then shut off and the slurry is cooled as quickly as possible in the consistometer to 194 F (90 C), if at a temperature above 1940F (900C), while it is maintained in a static condition. If the shear pin on the drive motor shears off at any time, the test is terminated. The pressure then is released from the slurry cup and the sample is inspected for excessive settling by pushing a rod to the bottom of the test chamber to locate the level of settled solids.If excessive resistance is encountered in pushing the rod through the sample, the rod will not go through the sample or the shear pin sheared prior to completion of the three static test periods, the cement slurry is considered to exhibit too much solids separation and is unacceptable for use. A small amount of light settling or fluid separation at the top of the sample cup is acceptable in most situations and would not effect performance of the cement slurry when introduced into a subterranean formation. The results of the various tests are set forth below: The quantities set fourth in percent are percent by weight of a 941b sack (42.5kg) of cement. The quantities in US gallons are US gallons per 941b sack of cement (lgal/sack is .09m3/kg).

Slurrv Composition 1 Class H cement, 35% SSA-2 1., 60E hematite, 0.1% CMHEC 2., 0.05 gal (0.19dm3) D-Air 3 3., 0.143 gal (0.54dm3) CFR-2L 4., 0.3 gal (1.14 dm3) HR -12L 5., 3 gal (11.4 dm3) 25/75 styrene/butadiene latex, 0.338 gal (1.28 dm3) surfactant (35% active), 2.55 gal (9.66 dm3) water.

Slurry weight 18.5 Ib/gal (2216 kg/m3).

Slurry Composition 2 Class H cement, 35% SSA-2, 60% hematite, 0.2% CMHEC, 0.05 gal D-Air 3, 0.143 gal. CFR-2L, 0.27 gal, HR 12L, 2 gal. 25/75 styrene/butadiene latex, 0.23 gal, surfactant, 3.68 gal. water. Slurry weight 18.5 lb/gal (2216 kg/m3).

Slurrv comPosition 3 Class H cement, 35% SSA-1 6 , 60% hematite, 0.15% CMHEC, 0.05 gal, D-Air 3, 1% SCR-100 7., 0.18 HR -13L 8 , 2.5 gal. 25/75 styrene/butadiene latex, 0.25 gal.

surfactant, 3.37 gal. water. Slurry weight 18.5 lb/gal (2216 kg/m3).

Slurry Composition 4 Class H cement, 35% SSA-2, 60% hematite, 0.3% CMHEC, 0.05 gal. D-AIR 3, 0.143 gal. CFR-2L, 0.32 gal. HRe-12L, 2.5 gal. 25/75 styrene/butadiene latex, 0.2 gal. surfactant, 3.17 gal. water. Slurry weight 18.5 lb/gal. (2216 kg/m3!.

Slurry Composition 5 Class H cement, 35% SSA -1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 0.143 gal. CFR 2-L, 0.3 gal. HR#-12L, 2.5 gal. 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.14 gal. water. Slurry weight 18.5 lb/gal. (2216 kg/m3).

Slurry Composition 6 Class H cement, 35% SSA-1, 608 hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 1% SCR-100, 0.16 gal. HR#-13L, 2.5 gal. 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.39 gal.

water. Slurry weight 18.5 lb/gal . (2216 kg/m3).

Slurry Composition 7 Class H cement, 35% SSA-1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0t SCR-100, 0.38 gal. HR#-13L, 2.4 gal 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 2.96 gal water. Slurry weight 18.7 lb/gal. (2240 kg/m).

Slurry Composition 8 Class H cement, 35t SSA-1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.32 gal. HR#-13L, 2.5 gal.

25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.0 gal. water Slurry weight 18.7 lb/gaL (2240 kg/m3).

Slurry Composition 9 Class H cement, 35% SSA-1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.28 gal. HR-13L, 2.5 gal 25/75 styrene/butadiene latex, 0.25 gal. surfactant, 3.29 gal.

water. Slurry weight 18.5 lb/gal. (2216 kg/m ).

Slurry Composition 10 Class H cement, 35% SSA-1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 1% SCR-100, 0.35 gal. HRe-13L, 2.5 gal 25/75 styrene/butadiene latex, 0.25 gal surfactant, 3.24 gal.

water. Slurry weight 18.5 lb/gal. (2216 Slurry Composition 11 Class H cement, 35% SSA-1, 60% hematite, 0.15% CMHEC, 0.05 gal. D-AIR 3, 2.0% SCR-100, 0.5 gal HR -13L, 2.5 gal 25/75 styrene/butadiene latex, 0.3 gal surfactant, 3.07 gal.

water. Slurry weight 18.5 lb/gal. (2216 kg/m ).

1. SSA-2 : graded silica sand 40-200 mesh (aperture .42mm-.074mm) 2. CMHEC : carboxymethylhydroxyethyl cellulose 3. D-AIR 3 : commercially available defoamer from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 4. CFR-2L : naphthalene sulfonic acid condensed with for maldehyde (33% active) 5. HR# 12L : high temperature lignosulfonate retarder commer cially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 6.SSA-1 : graded silica sand 140-400 mesh (aperture 0.0105-.037nn) 7. SCR-100 : AMPS#/acrylic acid copolymer retarder commer cially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 8. HR-13L : high temperature lignosulfonate retarder commercially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 TABLE I Atmospheric VG Farn Reedings, Free Fluid Loss 24 hour Slurry Temp. Consistometer, Bc RPM Water, at temp. FHCT Solids Compressive No.F. (C) Initial Final 300 200 100 6 3 % by &alpha;/ Thickening Suspension strenght vol. 30 min. time Capability 350 F(177 C) 290 F(143 C) 80 (27) 215 149 84 13 10 0 1 190 (88) - - 151 103 59 08 05 - 272 (133)- - - - - - - - 0 20 4 : 06 pass 80 (27) 7 9 176 125 72 14 12 0 2 190 (88) - 110 76 44 08 07 - 272 (133)- - - - - - - 33 3 : 34 pass 2100 1500 80 (27) 17 17 300+ 240 140 27 21 0 3 190 (88) 12 07 114 77 43 07 06 - 292 (133) - - - - - - - 0 38 4 : 44 pass 4430 3120 80 (27) 15 16 300+ 233 142 33 28 0 4 190 (88) - - 102 74 49 17 15 - 292 (133)- - - - - - - 0 31 4 : 11 pass 2300 1100 80 (27) 15 15 300+ 216 124 26 22 0 5 190 (88) 12 07 135 98 57 11 09 292 (133)- - - - - - - 0 68 4 : 34 pass 2960 4400 80 (27) 18 17 300+ 269 156 30 24 0 6 190 (88) 14 07 145 191 55 09 07 292 (133)- - - - - - - 0 44 3 : 55 pass 5120 2880 TABLE I (Continued) Atmospheric VG Farn Reedings, Free Fluid Loss 24 hour Slurry Temp. Consistometer, Bc RPM Water, at temp. FHCT Solids Compressive Nb. F.(C) Initial Final 300 200 100 6 3 % by &alpha;/ Thickening Suspension strenght vol. 30 min. time Capability 400 F (204 C) 350 F (177 C) 80 (27) - - 300+ 300+ 248 78 65 0 7 190 (88) - - 197 135 80 06 12 - 358 (133)- - - - - - - 0 21 4 : 34 pass 4150 2900 80 (27) 30 300+ 300+ 275 68 52 0 8 190 (88) 29 12 235 168 96 18 15 358 (133)- - - - - - - - 34 3 : 55 pass 5220 3250 80 (27) 16 16 300+ 274 171 39 35 0 9 190 (88) 15 09 148 105 61 12 10 358 (133)- - - - - - - 0 20 4 : 02 pass 3840 248 80 (27) 17 17 300+ 232 139 30 25 0 10 190 (88) 16 122 86 49 09 07 - 372 (133)- - - - - - - 0 38 4 : 33 pass 4680. 3860 80 (27) 31 29 300+ 300+ 222 57 49 0 11 190 (88) 18 09 176 129 75 15 11 - 392 (133)- - - - - - - 0 27 4 : 05 pass 3650. 2220 1. at 415 F.

2. at 425 F.

The following test was performed to determine the acid resistance of the cement slurry formed in accordance with the present invention.

Test slurries were prepared as in Example I. A sample of the slurry was placed in a 2 x 2 x 2 inch (5.1 x 5.1 x 5.1 cm) mold and allowed to cure for 96 hours at 2000F (930C). The cube then was removed from the mold, weighed and placed in a solution of 12% HC1/3% HF maintained at 1900F (880C) for 1 hour. The percentage (%) of mass lost from the cube then was determined. The slurries utilized and the results of the tests are set fourth below: Slurrv ComPosition 1 Class H cement, 5% Microbond HT 1 , 2% bentonite, 0.5% CFR-3 2 , 0.3 gal (1.14 dm3) surfactant, 0.2 gal (0.76 dm3) D-AIR 3, 2 gal (7.6 dm3) 25/75 styrene/butadiene latex, 3.7 gal (14.1 dm3) water.

Slurry Composition 2 Class H cement, 5% Microbond HT, 2% bentonite, 0.5% CFR-3, 0.1% HR -5 3., 0.3 gal (1.14 dm3) surfactant, 0.2 gal (0.76 dm3) D-AIR 3, 2 gal (7.6 dm3) 25/75 styrene/butadiene latex, 3.7 gal (14.1 dm3) water.

Slurry weight of each sample 15.3 lb/gal(i833 kg/m3) Fluid loss at thickening Mass loss 4 day Slurry 175 F (79 C) 1000 time 190 F (88 C) compressive No. (cc/30 min) (hr:min) (% by wt. ! strength (psi) 1 31 2:58 4.0 3200422MPa) 2 - 5:37 0.0 3470 (23.9MPa) 1. Microbond HT : cement expansion additive commercially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 2. CFR-3 : cement dispersant additive commercially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 3. HRe-5 : sodium lignosulfonate retarder commer cially available from HALLIBURTON SERVICES, Duncan, Oklahoma 73536 4. : Strength obtained after acidizing treatment The foregoing test results clearly indicate the effectiveness of the fluid-loss control achieved by the composition of the present invention.

Claims (7)

1. A cement slurry composition having improved fluid loss control properties, which comprises a hydraulic cement, water, a styrene/butadiene latex and a surfactant, wherein the latex is present in the composition in an amount of from about 4 to about 35 percent latex by weight of said hydraulic cement, and the weight ratio of styrene to butadiene in said latex is from about 20 to 80 to about 30 to 70; the surfactant is a compound having the general formula H(CH2)d ( C2H4)e SO3 X wherein X is any compatible cation, d is from about 5 to about 20 and e is from about 10 to about 30, said surfactant being present in said composition in an amount of from about 5 to about 40 percent surfactant by weight of said latex; and said water is present in said composition in an amount of from about 20 to about 150 percent water by weight of said hydraulic cement.

2. A composition according to claim 1, wherein said surfactant is present in an amount of from about 10 to about 25% surfactant by weight of said latex.

3. A composition according to claim 2, wherein said latex is present in an amount of from about 15 to about 25% latex by weight of said hydraulic cement.

4. A composition according to claim 1, 2 or 3, wherein said surfactant is of the general formula H(CH2)d ( C2H4)e S03 X wherein X is sodium, d is from about 12 to about 15 and e is about 15.

5. A composition according to claim 4, which further includes a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid in a mole ratio having from about 40 to about 60 mole percent 2-acrylamido-2methylpropanesulfonic acid with the balance comprising acrylic acid or salts thereof and said copolymer has a molecular weight below about 5000.

6. A cement slurry composition substantially as herein described in any of the Examples.

7. A method of cementing a conduit in a wellbore penetrating a subterranean formation comprising introducing a cement slurry composition into the annulus between said conduit and said formation and permitting said cement slurry to set, the temperature of said formation being from about 300F (-10C) to about 4500F (2320C) and contains gas under pressure wherein the cement slurry composition is as claimed in any of claims 1 to 6.